This invention relates generally to intravenous infusion procedures wherein fluid is gravity-fed from a fluid container to a patient, and in particular to an alarm system for indicating when the container is exhausted.
The intravenous infusion of fluids by gravity flow is now a common procedure in modern hospitals. Among the fluids administered are plasma, blood, glucose and saline solutions. Intravenous injection over a protracted period is usually carried out by reducing fluid flow from the elevated container to a succession of discrete drops. This is effected by means of a drop chamber coupled to the output of the container through a drip tube. In practice, a delivery pipe is extended from the drop chamber to a lower position where the fluid is to be injected into the patient through a hollow needle or catheter.
It is often of vital importance that the fluid bottle or container be replaced with a fresh supply when the container is drained. This requires regular attendance or frequent inspection by a nurse or hospital orderly. Should an emergency arise or other factors come into play distracting the attention of the nurse or orderly, the container may become empty and remain unchanged. In some instances, failure to continue the supply of fluid may be fatal or harmful to the patient. Because the fluids being administered frequently contain life-giving drugs such as insulin, anti-biotics, vitamins, hormones or electrolytes, the failure to continue intravenous therapy, regardless of its cause, may have catastrophic consequences. With existing shortages of qualified hospital personnel, such failures are not uncommon.
Various types of monitoring or alarm systems have heretofore been devised to signal when the fluid being received by a patient from a container has drained to a low level. A typical alarm system for this purpose makes use of a spring by which the fluid container is suspended from an elevated support. As the fluid discharges and the weight of the container diminishes, the amount of spring extension is reduced to a point at which an electrical switch mounted at a preset position, is caused to close, thereby activating an alarm signal serving to alert the nurse to take whatever action is then appropriate.
The characteristics of the weighing spring and the related arrangement of parts must be preselected in accordance with the weight of the container load. Thus, the spring arrangement for a 500 ml. bottle of blood is necessarily different from that dictated by a 250 ml. bottle. A spring weighing arrangement is therefore not a universal monitor for any type of container, but is limited to a specific fluid load. Moreover, it is cumbersome and unreliable.
Other known forms of monitoring or warning devices for use in conjunction with intravenous flow arrangements, include electrical networks, oscillators, amplifiers and other elaborate circuits connected to the output of capacitative, electro-optical and other sophisticated forms of sensors. For example, in one such device which is attachable to the exterior of the fluid container to indicate when it is nearly empty, a capacitance bridge is provided, two of whose capacitances have dielectrics defined by the fluid in this container. When fluid falls to a given level, the resultant bridge output activates a nurse's call system or alarm.
Apart from the complexity and high cost of known types of electrical alarm systems, there is the further problem of safety, for intravenous infusion is sometimes conducted within an oxygen tent in which electrical sparking cannot be tolerated. Prior systems fail to provide adequate protection against sparking or high voltage shorts that may lead to sparking and fatal explosions.